Recovery of tertiary butyl alcohol

ABSTRACT

A process for the dimerization of isobutene wherein tertiary butyl alcohol is used to enhance the selectivity of the catalyst to the dimer is disclosed wherein the tertiary butyl alcohol is removed from the diisobutene product by water wash. The water/TBA stream is then subjected to reextraction to remove the TBA for recycle to the dimerization reactor. The dimerization is preferably carried out in a reactor wherein the pressure is controlled to maintain the reaction mixture at is boiling point. Additional dimerization is carried out in a distillation column reactor that acts as a debutanizer to separate the unreacted isobutene form the product and the tertiary butyl alcohol.

This application claim benefits of provisional application Ser. No.60/271,290 filed Feb. 23, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a process for the productionof diisobutene (DIB) wherein tertiary butyl alcohol (TBA) is used tomodify an acid catalyst to provide more selectivity to the dimer. Moreparticularly the invention relates to a process wherein the TBA and DIBare removed together as bottoms from a debutanizer column.

2. Related Art

One process for the dimerization of isobutene over an acid catalyst inthe presence of tertiary butyl alcohol is disclosed in U.S. Pat. No.4,100,220. The tertiary butyl alcohol is said to dehydrate the catalystand provide for improved selectivity to the dimer.

Another liquid phase process for the oligomerization of C₄ and C₅isoolefins is disclosed in U.S. Pat. No. 5,003,124 wherein the reactionmixture is allowed to boil to remove the heat of reaction and a furtherdimerization is obtained in a reactive distillation column. U.S. Pat.No. 4,242,124 discloses the reaction of isobutene with itself in acatalytic distillation column reactor to form diisobutene.

When tertiary butyl alcohol is used to improved the selectivity andseparated from the unreacted C₄'s by fractional distillation, then allcomponents boiling heavier than C₄ and lighter than DIB (referred to asheavies) may be removed along with the TBA and an azeotropic mixture ofDIB. Since most feeds have at least some of these heavies, their buildup must be prevented in the TBA recycle loop. A purge necessarilycontaining some TBA and DIB product is preferably withdrawn from the TBAloop. The purge represents a loss of isobutene (as TBA), a loss of feedheavies which might otherwise join the DIB in the gasoline pool, andsome DIB product itself. Thus, the removal of the TBA from the DIB andheavies would be desirable.

SUMMARY OF THE INVENTION

Briefly the present invention comprises the removal of TBA from a firsthydrocarbon stream into a water stream by contacting said streams underconditions of temperature and pressure to achieve extraction of said TBAinto said water stream, and preferably the recovery of said TBA fromsaid water stream by contacting said water steam containing said TBAwith a second hydrocarbon stream under conditions of temperature andpressure to achieve extraction of said TBA into said second hydrocarbonstream. In a further preferred embodiment the TBA is a process enhancerin a process from which the first hydrocarbon stream originates and in astill further preferred embodiment the second hydrocarbon stream is afeed to the process from which the first hydrocarbon stream originates.Thus in a most preferred embodiment the TBA enhancer is removed from theproduct hydrocarbon stream of a process by contact with water into thewater and then removed from the water by contact with the hydrocarbonfeed into the hydrocarbon feed to the process from which the firsthydrocarbon stream originated.

As used herein the term “TBA enhancer” means the TBA has a favorableeffect on the process in question. The TBA may act as a homogeneouscatalyst or catalyst modifier, although it may not be a reactant in theprocess. The TBA is present in very small amounts, usually in molaramounts of less than the reactant material, preferably a mol ratio of0.001 to less than 1 mol of TBA/mol of reactants.

In a particular embodiment the present invention comprises thedimerization of isobutene over an acid catalyst in the presence oftertiary butyl alcohol (TBA). After the product diisobutene (DIB) andTBA has been separated from the unreacted C₄'s, the bottoms containingthe TBA, DIB and heavies are washed with water in a liquid/liquidcontact column to remove the TBA in the water phase. The DIB and heaviesmay then be sent to gasoline blending or for further processing. TheTBA/water stream is then reextracted with a hydrocarbon stream,preferably C₄ feed, to remove and recycle the TBA.

The dimerization reaction may be effected in a standard single passdownflow fixed bed reactor, a distillation column reactor or combinationas disclosed in U.S. Pat. No. 5,003,124 which is hereby incorporated byreference.

The term “reactive distillation” is used to describe the concurrentreaction and fractionation in a column. For the purposes of the presentinvention, the term “catalytic distillation” includes reactivedistillation and any other process of concurrent reaction and fractionaldistillation in a column, i.e., a distillation column reactor,regardless of the designation applied thereto.

The catalyst beds as used in the present invention may be described asfixed, meaning positioned in a fixed area of the column and includeexpanded beds and ebulating beds of catalysts. The catalysts in the bedsmay all be the same or different so long as they carry out the functionsof dimerization and hydrogenation as described. Catalysts prepared asdistillation structures are particularly useful in the presentinvention.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a flow diagram in schematic form of one embodiment of theinvention.

FIG. 2 is a flow diagram in schematic form of another embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Isobutene is dimerized to diisobutene according to the followingreaction:

Isobutene+Isobutene←→Diisobutenes  (1)

The dimerization of isobutene with itself is of particular interestbecause either of the isomers of diisobutene produce 2,2,4-trimethylpentane (isooctane) when hydrogenated. If a catalytic distillationreactor is used the catalytic material employed in the process ispreferably in a form to serve as distillation packing. Broadly stated,the catalytic material is preferably a component of a distillationsystem functioning as both a catalyst and distillation packing, i.e., apacking for a distillation column having both a distillation functionand a catalytic function. The catalyst is prepared in the form of acatalytic distillation structure.

The dimerization catalyst may include either an acidic cation exchangeresin or zeolite, which are generally employed as fine powders.Structures for this use are described in U.S. Pat. Nos. 4,215,011;4,302,356; 4,443,559; 5,266,546 and 5,348,710 which are incorporatedherein. Other catalytic distillation structures useful for this purposeare disclosed in U.S. Pat. Nos. 4,731,229; 5,073,236; 5,431,890 and5,730,843 which are also incorporated by reference.

The mole sieve or cation exchange resin catalyst packing is of such anature as to allow vapor flow through the bed, yet provide a sufficientsurface area for catalytic contact as described in the previously notedpatents. The catalyst packing is preferably arranged in the upperportion of the distillation column reactor, more preferably occupyingabout one-third to one half of the column. A rectification section maybe located above the catalyst zone.

To provide the desired degree of temperature and residence time control,a process and apparatus are provided wherein the reaction liquid isboiling within a distillation column reactor. Overheads are withdrawnand condensed with some of the condensate being returned to thedistillation column reactor as reflux. The advantage of the presentprocess is that due to the continual reflux a portion of the selecteddimer (diisobutene) is always condensing on the catalyst structure.

Several different arrangements have been disclosed to achieve thedesired result. For example, British Patents 2,096,603 and 2,096,604disclose placing the catalyst on conventional trays within adistillation column. A series of U.S. patents, including those listedabove and more, particularly U.S. Pat. Nos. 4,443,559 and 4,215,011disclose using the catalyst as part of the packing in a packeddistillation column. The use of multiple beds in a reaction distillationtower is also known and illustrated, for example, in U.S. Pat. Nos.4,950,834; 5,321,163; and 5,595,634.

The catalyst component may take several forms. In the case ofparticulate catalytic material, generally from 60 mm to about 1 mm downthrough powders, is enclosed in a porous container such as screen wireor polymeric mesh. The material used to make the container must be inertto the reactants and conditions in the reaction system. The screen wiremay be aluminum, steel, stainless steel, and the like. The polymer meshmay be nylon, Teflon, or the like. The mesh or threads per inch of thematerial used to make the container is such that the catalyst isretained therein and will not pass through the openings in the material.Catalyst particles of about 0.15 mm size or powders may be used andparticles up to about ¼ inch diameter may be employed in the containers.

In the present process the first hydrocarbon stream containing TBA maybe contacted with the water stream in either concurrent orcountercurrent flow. The contacting may be carried out at pressuresranging from subatmospheric to superatmospheric and at temperaturesranging from ambient to several hundred degrees C., preferably 50 to 200psig and more preferably 75 to 125 psig at 20 to 40° C.

The contact of the TBA containing water stream may be contacted with thesecond hydrocarbon stream under the same range of conditions of pressureand temperature as the first contact which favor the removal of the TBAto the second hydrocarbon stream.

In addition to the conditions of temperature and pressure, the masstransfer effect of the extractions may be enhanced by having theextracting liquid (water or hydrocarbon) present in a volume excess tothe extractant liquid (the liquid containing TBA, from which TBA is tobe removed, either water or hydrocarbon), preferably from about 1 to 5volumes of extracting liquid per volume of extractant liquid. Referringnow to FIG. 1 a simplified flow diagram of one embodiment of theinvention is shown. The feed containing the isobutene to be dimerizedand TBA is fed via flow line 101 to a reactor 10 containing a bed ofacidic cation exchange resin 12. The effluent from the reactor in flowline 103 is fed to a debutanizer 20 containing vapor/liquid contactstructures 22 where the C₄ and lighter material is taken overheads viaflow line 104. The material in flow line 104 may be recycled as feed ifdesired (not shown). The bottoms from the debutanizer containing productDIB, TBA and heavies (other hydrocarbon material boiling heavier thanC₄) are taken via flow line 105 and fed to water wash column 30containing liquid/liquid contact structures 32 where it is contactedwith water fed near the top by flow line 106. The product DIB is takenas overheads from this column via flow line 107 and the liquid waterphase containing the TBA is taken as bottoms via flow line 108. Thebottoms in flow line 108 is fed to extraction column 40 containingliquid/liquid contact structure 42 where it is contacted withhydrocarbon feed containing the isobutene. The water is removed asbottoms via flow line 110 and may be recycled to column 30 (not shown).The hydrocarbon feed containing the isobutene and TBA is then recycledto the reactor via flow line 111 and 103. If desired all of the feed inline 101 may also be fed to the extraction column 40 where the feed willbe water washed to remove contaminants. Generally all of the feed iswater washed (not shown).

Referring now to FIG. 2 a simplified flow diagram of a second embodimentis shown. All of the components are numbered the same as FIG. 1 for easeof reference. The only difference between the embodiments is that a bed24 of acid ion exchange catalyst is placed within the debutanizer 20where further reaction of isobutene with itself to form additional DIBoccurs concurrently with the separation of unreacted isobutene and otherC₄ and lighter components which are taken as overheads via flow line104. The bottoms from the debutanizer containing product DIB, TBA andheavies (other hydrocarbon material boiling heavier than C₄) are takenvia flow line 105 and fed to water wash column 30 containingliquid/liquid contact structures 32 where it is contacted with water fednear the top by flow line 106. The product DIB is taken as overheadsfrom this column via flow line 107 and the liquid water phase containingthe TBA is taken as bottoms via flow line 108. The bottoms in flow line108 is fed to extraction column 40 containing liquid/liquid contactstructure 42 where it is contacted with hydrocarbon feed containing theisobutene. The water is removed as bottoms via flow line 110 and may berecycled to column 30 (not shown). The hydrocarbon feed containing theisobutene and TBA is then recycled to the reactor via flow line 111 and103. If desired all of the feed in line 101 may also be fed to theextraction column 40 where the feed will be water washed to removecontaminants. Generally all of the feed is water washed (not shown).

Preferably the reactor 10 is operated at a pressure such that themixture is boiling at between 120 and 300° F. whereby a portion but lessthan all of the mixture is vaporized, said reaction occurring in theliquid phase. This allows the heat of reaction to be absorbed by theboiling liquid without any increase in reaction temperature.

The invention claimed is:
 1. In a process for the dimerization ofisobutene to diisobutene wherein tertiary butyl alcohol is included inthe feed to the dimerization to improve the selectivity to dimer and theunreacted feed is separated from the product diisobutene and tertiarybutyl alcohol, the improvement comprising removing the tertiary butylalcohol from the diisobutene product by water washing to form a waterwash product.
 2. The process according to claim 1 further comprising thestep of extracting the tertiary butyl alcohol from the water washproduct with hydrocarbon and recycling the tertiary butyl alcohol to theprocess.
 3. The process according to claim 2 wherein said hydrocarbon isthe feed to the process.
 4. A process for the dimerization of isobuteneto form diisobutene comprising the steps of: (a) feeding a streamcontaining isobutene and tertiary butyl alcohol to a reactor containingan acidic catalyst; (b) reacting a portion of said isobutene with itselfin said reactor to form diisobutene; (c) feeding the effluent from saidreactor containing unreacted isobutene, diisobutene and tertiary butylalcohol to a fractional distillation column wherein unreacted isobuteneis separated from diisobutene and tertiary butyl alcohol; (d) removingunreacted isobutene from said fractional distillation column asoverheads; (e) removing diisobutene and tertiary butyl alcohol from saidfractional distillation column as bottoms; (f) washing said bottoms withwater to remove the tertiary butyl alcohol in a water phase; (g)extracting the tertiary butyl alcohol from said water phase with ahydrocarbon to form a hydrocarbon containing said extracted tertiarybutyl alcohol; and (h) recycling said tertiary butyl alcohol to saidreactor.
 5. The process according to claim 4 wherein the hydrocarbon ofstep (g) contains isobutene and said hydrocarbon containing saidextracted tertiary butyl alcohol is fed to said reactor.
 6. The processaccording to claim 4 wherein said reactor the pressure in said reactoris maintained such that the reaction mixture contained therein is at itsboiling point such that the heat of reaction is absorbed by the boilingliquid in the reactor.
 7. The process according to claim 4 wherein saidfractional distillation column contains a bed of acidic catalyst suchthat additional isobutene is reacted with itself to form additionaldiisobutene concurrently with said separation.
 8. A process for thedimerization of isobutene to form diisobutene comprising the steps of:(a) feeding a stream containing isobutene and tertiary butyl alcohol toa reactor containing an acidic catalyst; (b) reacting a portion of saidisobutene with itself in said reactor to form diisobutene whilemaintaining the reactor pressure such that the mixture within saidreactor is boiling in the range of 120 to 300° F. whereby a portion butless than all of the mixture is vaporized, said reaction occurring inthe liquid phase; (c) feeding the effluent from said reactor containingunreacted isobutene, diisobutene and tertiary butyl alcohol to afractional distillation column containing a bed of acidic catalystwherein additional isobutene is reacted with itself to form diisobuteneand unreacted isobutene is concurrently separated from diisobutene andtertiary butyl alcohol; (d) removing unreacted isobutene from saidfractional distillation column as overheads; (e) removing diisobuteneand tertiary butyl alcohol from said fractional distillation column asbottoms; (f) washing said bottoms with water to remove the tertiarybutyl alcohol in a water phase; (g) extracting the tertiary butylalcohol from said water phase with a hydrocarbon stream containingisobutene; and (h) recycling said extracted tertiary butyl alcohol tosaid reactor.